This article analyses the rapid spread of syphilis in the eastern part of the Bangwato Reserve, Botswana, between 1930 and 1950. The author argues that cultural factors, which entitled men to have multiple concurrent sexual relations, undermined ideas of morality and marital fidelity, thus aiding the transmission of venereal diseases. Social factors such as rural-urban migration further enhanced these effects. Notes, ref. [ASC Leiden abstract]